A semiconductor power converter includes a main circuit board installed in a housing of the semiconductor power converter. On the main circuit board, a main circuit converting power supplied from a power source to supply converted power to a load, and a first temperature sensor are disposed. The converter also includes a control circuit board installed in the housing. On the control circuit board, a control circuit controlling the main circuit, and a second temperature sensor are disposed. The converter further includes an internal-air-temperature estimation circuit that estimates an internal air temperature in the semiconductor power converter by using a temperature detected by the first temperature sensor and a temperature detected by the second temperature sensor.