Electroweak baryogenesis is a promising scenario to explain the origin of the baryon asymmetry of the Universe. In order to realize the scenario, the electroweak phase transition should be strongly first order. The sphaleron decoupling condition is the criterion for the strongly first-order electroweak phase transition. In this talk, we discuss the sphaleron decoupling condition in extended Higgs models. We show that upper bounds on masses of additional Higgs bosons can be obtained by utilizing the sphaleron decoupling condition and the unitarity bound. This talk is based on the papers [arXiv: 2005.05250, 2201.04791].