| 摘要 |
PROBLEM TO BE SOLVED: To improve a saturation current characteristics, related to a heterojunction field effect transistors, by suppressing running of a carrier in a parasitic channel. SOLUTION: The heterojunction field effect transistor comprises a semiconductor substrate 1, a buffer layer 2, a channel layer 5 comprising a semiconductor material having a band gap smaller than that of the buffer layer 2 (SiGe, SiGeC and the like), a cap layer 4 comprising a semiconductor marital having a band gap larger than that of the channel layer 5, a gate insulating film 5, a gate electrode 6, and source/drain regions 10 and 11. A carrier-injection preventing insulating part 9 is provided for electrically insulating at least the upper part of the cap layer 4 from the source/drain, so that injection of carriers into the parasitic channel is suppressed, while the carrier is preferably injected into the channel layer.
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