Safe operating area (SOA) in power semiconductors is one of the most important factors affecting device reliability. The SOA region of power MOSFETs must be well characterized for using in circuit design to meet the specification of applications, particularly including the time domain of circuit operations. In this paper, the characterization of SOA in the time domain is performed with the experimental measurement on silicon devices, and the useful techniques to improve SOA of power MOSFETs for using in high-voltage integrated circuits are overviewed.