IGBT Insulated gate bipolar transistor (IGBT) is a new high conductance MOS gate-controlled power switch. They are manufactured in a similar way to N-channel MOSFETs but employ an N-epitaxial layer grown on a P+ substrate. In operation the epitaxial region is conductivity modulated (by excess holes and electrons) thereby eliminating a major component of the on-resistance. For example, on-resistance values have been reduced by a factor of about 10 compared with those of conventional N-channel power MOSFET of comparable size and voltage capability. Tokentools welders employ IGBT transistors manufactured by Infineon and Siemens.