A semiconductor device exhibits low pressure loss and is capable of cooling a plurality of power semiconductor chips evenly. This semiconductor device includes a semiconductor module and a cooler for cooling a power semiconductor element mounted in the semiconductor module. A cooling unit of the cooler has a first header part that has a first bottom surface disposed between a coolant inlet and an end portion of a first substrate on the coolant outlet side and inclined toward a bottom plane of cooling fins so that a coolant supplied from the coolant inlet flows toward the cooling fins; and a second header part that has a second bottom surface inclined from an end portion of the bottom plane of the cooling fins on the coolant outlet side so that the coolant discharged from the cooling fins flows to the coolant outlet.