Shares of asset manager Apollo Global Management (APO) and human resources software provider Workday (WDAY) are surging more than 5% and 8%, respectively, in premarket trading Monday on news the companies will become the newest members of the S&P 500 Index. 

S&P Global Indexes announced on Friday that the two firms would be added to the prestigious index at the opening of trading on Dec. 23.

They will replace radio frequency semiconductor maker Qorvo (QRO) and defense technology company Amentum Holdings (AMTM). Both Qorvo and Amentum Holdings will move into the S&P SmallCap 600 Index, replacing employment services firm Kelly Services (KELYA) and real estate investment trust (REIT) Service Properties Trust (SVC), respectively. 

Joining the S&P 500 often gives a company's stock price a boost because the shares can be added to various index-tracking funds, giving them more exposure to investors.

Shares of Apollo Global Management have been on a tear this year, soaring 90% to an all-time high. Workday shares have been little changed year-to-date.