The reconstruction and the step structure change during the phase transition on an InAs(001) surface under As pressure is observed directly by using scanning electron microscopy. The domain formation corresponding to the first‐order phase transition is clearly seen as predicted by Monte Carlo simulation with a lattice gas model. It is also seen that the step structure largely depends on the surface reconstruction and the misorientation direction. This gives the first observation of phase‐transition‐induced step bunching on a compound semiconductor surface. ©1995 American Institute of Physics.