Abstract: A resonant power converter includes a positive bus line (1A) and a negative bus line (1B). A power converting portion (2) connected between a DC power source (1) and a load (5) operates for implementing power conversion. The power converting portion includes a plurality of main switching devices (3a-3f) connected in series and provided between the positive bus line and the negative bus line, and a plurality of flywheel diodes (4a-4f) connected in antiparallel with the main switching devices respectively for each phase. A resonant circuit (8) connected between the positive bus line and the negative bus line includes a resonant capacitor (6) and a resonant reactor (7) connected in series with the resonant capacitor. A control device (13) operates for switching the main switching devices in accordance with a predetermined pattern to enable the power converting portion to implement power conversion.

Abstract: An inverter portion (2) includes upper main switches and lower main switches of different phases, main switching devices (3a-3f) provided in the upper main switches and the lower main switches respectively, and diodes (4a-4f) connected in antiparallel with the main switching devices (3a-3f) respectively. Bus-splitting portions (1D, 1E, 1F, 6, 7) are connected to each other at a bus-splitting junction. A resonant circuit portion (8) includes resonant reactors (9a-9c), auxiliary switches (11a-11c), and resonant capacitors (10a-10c). The resonant reactors (9a-9c) and the auxiliary switches (11a-11c) are connected in series circuits. The series circuits are connected between the bus-splitting junction and the junctions between series-coupled main switches. The resonant capacitors (10a-10c) are connected in parallel with the series circuits respectively.

Abstract: On the surface of a semiconductor substrate there are formed a silicon oxide film, silicon nitride film and resist, whereby a groove is formed in the semiconductor substrate through an opening portion by chemical dry etching. An oxide film is formed on the inner surface of the groove by wet oxidation and, further, this oxide film is removed by wet etching, after which the surface of the semiconductor substrate located on the outer-peripheral side of the groove from an angular portion defined between a side surface of the groove and the surface of the semiconductor substrate is exposed. Then, the inner surface of the groove and the exposed surface of the semiconductor substrate are oxidized to thereby form a LOCOS oxide film, and thereafter this LOCOS oxide film is removed. As a result of this, the angular portion is made round, thereby enabling the avoidance of the concentration of an electric field on the angular portion of the groove.