Requirement Rule 4420 (c) Under this requirement companies must have at least $75 million in total assets, total revenue, or listed securities. Listed securities as defined by the Nasdaq are securities listed on either a Nasdaq or another national exchange. The market value of the shares upon listing must be worth at least $20 million. They are also required to add an additional market maker for a total of four market makers.
A company has three ways to get listed on the Nasdaq depending on the underlying fundamentals of the company. If a company does not meet certain criteria such as the operating income minimum, it has to make it up with larger minimum amounts in another area like revenue. This helps to improve the quality of companies listed on the exchange.
It doesn't end there: after a company gets listed on the market, it must maintain certain standards to continue trading. Failure to meet the specifications set out by the stock exchange will result in its delisting. Falling below the minimum required share price, or market capitalization, is one of the major factors triggering a delisting. Again, the exact details of delisting depend on the exchange.
(For further reading on the Nasdaq and other U.S. exchanges, see Getting to Know Stock Exchanges and The Tale Of Two Exchanges.)