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For 4H-SiC mosfets, the parasitic PiN body diode causes problems such as significant forward voltage drop of body diode and poor reverse recovery characteristics during high-temperature operation. A reasonable solution is a mosfet with an integrated Schottky barrier diode to deactivate the PiN body diode. Since SiC mosfets can operate at extremely high temperatures, the characterization of electrical parameters at high temperatures and changing with the temperature are very important for high power applications and system reliability. However, there is a lack of comparison and analysis of the two devices on electrical properties at ultrahigh temperatures. In this article, a 1.2 kV conventional mosfet and a mosfet integrated with a junction barrier Schottky diode (JBSFET) were fabricated with a consistent process flow. In the temperature range from 300 to 575 K, analytical models of the temperature-dependent electrical parameters of these two devices were established and compared, which were successfully verified by the measurements. These models can provide guidance for ultrahigh temperature applications of JBSFETs. Temperature-related expressions can also be used for junction temperature monitoring of temperature-sensitive electrical parameters. Experimental results show that JBSFET has better third quadrant conduction characteristics and higher temperature stability below 450 K, but loses obvious performance advantages at 575 K. So, the recommended operating temperature range of JBSFET is from 300 to 450 K. Finally, the continuous operation performance of the body diodes in buck converters is analyzed. The higher efficiency of buck converter based on JBSFET's body diode indicates its great application potential in compact converters, especially in the recommended temperature range.