Goldman Sachs is planning an IPO of 6M shares for specialty lending unit Goldman Sachs BDC

Goldman Sachs is preparing an initial public offering of its specialty lending unit, Goldman Sachs BDC.

The bank is planning an IPO of 6 million shares and said underwriters will have an option to buy another 900,000 shares.

Goldman said in a regulatory filing Tuesday that it expects to price the offering next week in a range between $20 and $21 a share, which would raise $123 million at the midpoint. It will be listed on the New York Stock Exchange under the ticker symbol "GSBD."

Goldman Sachs BDC Inc. was formed in 2012. It is a management investment company with $1.27 billion in debt and equity investments as of Dec. 31.

Its primary business involves making investments in medium-size companies, according to regulatory filings. Its investments are typically worth $5 million to $50 million and mature in three to 10 years. It also makes speculative "opportunistic investments." Those investments are not rated, but the company says they would receive "junk" ratings if they were rated.

Shares of Goldman Sachs Group fell $5.22, or 2.8 percent, to $182.71 on Tuesday. The stock was up 54 cents in aftermarket trading.