Abstract: According to the present invention, a semiconductor device includes a semiconductor layer, a source electrode provided in the semiconductor layer, a drain electrode provided in the semiconductor layer and disposed away from the source electrode, a first gate electrode provided between the source electrode and the drain electrode and a second gate electrode provided between the source electrode and the drain electrode, the second gate electrode having at least a part thereof located closer to the drain electrode than the first gate electrode. The semiconductor layer includes a first facing part that is a part facing the first gate electrode; and a second facing part that is a part facing the second gate electrode. The first facing part does not conduct when a first gate voltage is 0 V or less. The second facing part does not conduct when a second gate voltage is 0 V or less.

Abstract: According to the present invention, a semiconductor device includes a semiconductor layer, a source electrode provided in the semiconductor layer, a drain electrode provided in the semiconductor layer and disposed away from the source electrode, a first gate electrode provided between the source electrode and the drain electrode and a second gate electrode provided between the source electrode and the drain electrode, the second gate electrode having at least a part thereof located closer to the drain electrode than the first gate electrode. The semiconductor layer includes a first facing part that is a part facing the first gate electrode; and a second facing part that is a part facing the second gate electrode. The first facing part does not conduct when a first gate voltage is 0 V or less. The second facing part does not conduct when a second gate voltage is 0 V or less.

Abstract: An RF level detector 33 adjusts an RF receive level according to a selected threshold, and a plurality of level detectors 31d to 31f detect the levels of signal waves so as to acquire signal wave detection levels, respectively. A C/N determining unit 26a detects a carrier-to-noise ratio for each of the signal waves, and outputs a C/N determination value as signal wave receive sensitivity. A microcomputer 32 selects the threshold which is provided to the RF level detector 33 according to the signal wave detection levels and the C/N determination values, and performs a receive control operation on a desired wave.