The semi-forcing notrump is a bidding convention in the card game of bridge.

In standard bidding, the response of 1 notrump to an opening bid of 1 of a suit shows 6 to 9 high card points and is non-forcing. Opener, with a balanced minimum, may pass the 1NT response and, if the opponents also pass, that will become the contract.

As a variation in the 2/1 game forcing system, some partnerships choose to play their 1 notrump response to 1 of a major suit as semi-forcing. The rebids and subsequent auctions are the same as with the forcing notrump, except: Opener is allowed to pass with a 5-3-3-2 minimum and no interest in game opposite a limit raise (including 3-card support for opener's major).

This changes follow-up auctions in that opener is assumed to either have 4 or more cards in any new suit bid, or some extra values when holding only 3 cards in a newly bid minor.