TradingKey – SK Hynix ( SKHY) has been listed on Nasdaq for over a week. On July 14, Eastern Time, its ADR price once traded at a premium of as high as 51% over its underlying shares in South Korea, before quickly retreating to around 19%. Since then, the premium did not continue to narrow, but instead widened again; on July 21, the ADR premium was approximately 29.8%. Such a glaring divergence in the pricing of the same company's shares across two markets is the result of the combined play of the ADR trading mechanism and arbitrage windows.

What Is an ADR? How to Calculate ADR Premium and Discount Rates

ADRs (American Depositary Receipts) are issued by US depositary banks and represent a specific number of shares in a foreign company. US investors do not need to open accounts in overseas markets, as they can invest in foreign companies directly through ADRs.

After purchasing the corresponding number of underlying shares in foreign markets, depositary banks package them into ADRs and issue them in the US stock market. SK Hynix listed on Nasdaq on July 10, issuing ADRs corresponding to approximately 17.79 million common shares (with each ADR representing 0.1 common shares) and raising about $26.5 billion, making it the largest US IPO by a foreign company. For US institutions, trading SK Hynix directly through Nasdaq is much more convenient than opening a South Korean stock account and completing cross-border settlement.

The formula for calculating the premium/discount rate is as follows:

Premium/Discount Rate = (Actual ADR Price × Conversion Ratio ÷ Exchange Rate - Local Benchmark Share Price) ÷ Local Benchmark Share Price × 100%

That is, the ADR price is converted into a per-share USD price based on the "number of local shares represented by each ADR," and then converted into the local currency at the spot exchange rate to be compared with the current price of the local underlying share. A positive result represents a premium, while a negative result represents a discount, reflecting market sentiment or arbitrage opportunities.

Why SK Hynix ADRs Have a High Premium?

On their first day of trading, SK Hynix ADRs closed up more than 12%, representing a premium of around 3% over the local Korean shares. By July 14, the premium had expanded to 51%.

[Source: Futu]

The immediate cause of this change is a supply-demand imbalance: buying demand from U.S. investors surged, while the number of tradable ADRs was limited, with buying pressure pushing prices higher. The premium is the result of a short-term supply-demand mismatch, rather than a fundamental repricing of SK Hynix by the market.

The arbitrage mechanism that limits the premium was not fully effective before July 29. The Korea Securities Depository (KSD) previously only allowed the one-way conversion of ADRs into local Korean shares without a reverse mechanism, meaning arbitrageurs could not quickly close the price gap by 'buying local shares and converting them into ADRs'.

Although KSD stated that it would accept two-way conversion applications starting July 29, the underlying new local shares corresponding to this ADR issuance are not expected to list in South Korea until July 29. Conversion applications can only be submitted after the new shares list, and the depositary bank, Citigroup ( C ), has not yet announced a specific conversion schedule. Moreover, the actual conversion involves procedures such as foreign exchange declarations, meaning it cannot be completed instantly on the day of application. Consequently, liquidity between the two markets was effectively segregated prior to July 29, and the actual opening of the arbitrage window is expected to occur after July 29.

On July 16, the premium fell from 51% to 19%, primarily because the market front-ran arbitrage expectations. Although the two-way conversion channel had not yet materially opened, investors had already begun pricing in the imminent implementation of the arbitrage mechanism. This, combined with profit-taking by some short-term capital, drove the rapid contraction of the premium.

On July 23, KSD confirmed that the initial quota for converting SK Hynix local shares into ADRs had been fully exhausted, with the conversion cap set at 2.5% of the company's total outstanding shares. This quota was entirely utilized during the July 10 IPO, meaning external investors currently cannot convert local shares into ADRs unless existing ADR holders first convert their ADRs back into local shares to free up quota. Consequently, the potential short-term supply of new ADRs is further restricted, and the premium could remain elevated or even widen further before the arbitrage window materially opens. Generally, the stricter the ADR conversion limit set by KSD, the higher the premium.

In addition, overall emerging market sentiment and Nasdaq liquidity will also affect the premium. If Samsung Electronics launches its own ADR in the future, U.S. investors will have another option in the Korean memory chip space, potentially diverting demand from SK Hynix ADRs and putting further pressure on the premium.

What ADR Discount and Premium Mean for Investors?

Discounts and premiums directly affect buying costs and selling returns. When the ADR premium exceeds 30%, the risk of chasing highs is significantly elevated; once arbitrage channels open, the premium may contract rapidly. A discount may reflect market concerns over the company's short-term prospects, but it could also represent a relatively undervalued buying opportunity.

Sometimes, premiums can also bring additional returns. If a company is about to be included in a core index like the Nasdaq 100, concentrated buying by passive funds may support the premium, allowing investors holding the ADRs to enjoy these gains.

Summary

ADRs provide U.S. investors with a convenient channel to participate in high-quality global companies, but the premium or discount directly determines the purchase cost and exit returns. The case of SK Hynix demonstrates that the higher a premium is pushed, the faster it tends to fall back once an arbitrage window opens—often quicker than expected. Before buying ADRs, it is recommended to check the premium/discount levels to avoid paying a price far higher than the underlying shares for the same company.

For reference, SK Hynix's current conversion restriction framework is highly aligned with that of TSMC ( TSM ), where TSMC ADRs can be converted one-way back into local Taiwan shares, but conversion from local shares to ADRs is strictly controlled, which is consistent with the logic of SK Hynix's 2.5% quota cap. Over the past five years, the average premium of TSMC ADRs over Taiwan-listed shares reached 12.6%. This case indicates that under similar restrictive structures, a certain level of premium may persist for the long term, rather than completely disappearing as soon as arbitrage opens. When evaluating SK Hynix ADRs, investors should incorporate such structural premiums into their long-term considerations.

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