A comparative study of the drain breakdown phenomena in junctionless (JL) and inversion mode (IM) p-channel MOSFETs has been investigated experimentally with different V GS , channel widths, and V SUB . In order to explain the dependence of drain breakdown voltages (BV DS ) on V GS , 3-D device simulation has been also performed. When the device is turned ON, the BV DS is larger in JL than IM transistors. The BV DS is decreased with the increase of |V GS | in IM transistors but it is increased in JL transistors. When the device is turned OFF, the BV DS is larger in IM than JL transistors. The BV DS is decreased with the increase of channel width for JL and IM transistors. The BV DS is decreased in IM transistor when the back surface state of Si film is changed from the accumulation to the inversion but it is almost constant in JL transistors.