  We discuss whether a multi-step electroweak phase transition (EWPT) occurs in
two Higgs doublet models (2HDMs). The EWPT is related to interesting phenomena
such as baryogenesis and a gravitational wave from it. We examine parameter
regions in CP-conserving 2HDMs and find certain areas where the multi-step
EWPTs occur. The parameter search shows the multi-step EWPT prefers the scalar
potential with the approximate $Z_2$ symmetry and a mass hierarchy between the
neutral CP-odd and CP-even extra scalar bosons $m_A<m_H$. By contrast, the
multi-step EWPT whose first step is strongly first order favors a mass
hierarchy $m_A>m_H$. In addition, we compute the Higgs trilinear coupling in
the parameter region where the multi-step EWPTs occur, which can be observed at
future colliders. We also discuss a multi-peaked gravitational wave from a
multi-step EWPT.
