An electronics device unit (10, 10A, 10B, 10C, 10D, 10E, 10F, 10G), comprising: a circuit board; a plurality of semiconductor components (20-1 to 23) that are dispersedly mounted on the circuit board, the plurality of semiconductor components generating heat, heat sinks (30-1 to 33) being mounted on the plurality of semiconductor components, respectively; and a cover member that is provided over the heat sinks to form a tunnel on the circuit board, a cooling medium flowing in the tunnel, wherein the plurality of semiconductor components are cooled via the heat sinks by a flow of the cooling medium travelling through the tunnel in a flow direction, and the plurality of semiconductor components are arranged on the circuit board in such an arrangement that in terms of a cross-section orthogonal to the flow direction, a ratio of a cross-sectional area of a clearance at a downstream part of the flow of the cooling medium to a cross-sectional area of the tunnel is smaller than a ratio of a cross-sectional area of a clearance at an upstream part of the flow of the cooling medium to the cross-sectional area of the tunnel, the cross-sectional area of the clearance at the upstream part being defined by subtracting from the cross-sectional area of the tunnel a cross-sectional area at the upstream part occupied by the heat sinks that block the flow of the cooling medium, the cross-sectional area of the clearance at the downstream part being defined by subtracting from the cross-sectional area of the tunnel a cross-sectional area at the downstream part occupied by the heat sinks that block the flow of the cooling medium, and wherein a place at which the plurality of the semiconductor components are mounted is divided into at least three regions with respect to a direction of the flow of the cooling medium, space parts (61, 60; 140, 141, 142) are formed between the at least three regions, respectively, and as the space part is located at the more downstream side, the space part becomes wider. a circuit board; a plurality of semiconductor components (20-1 to 23) that are dispersedly mounted on the circuit board, the plurality of semiconductor components generating heat, heat sinks (30-1 to 33) being mounted on the plurality of semiconductor components, respectively; and a cover member that is provided over the heat sinks to form a tunnel on the circuit board, a cooling medium flowing in the tunnel, wherein the plurality of semiconductor components are cooled via the heat sinks by a flow of the cooling medium travelling through the tunnel in a flow direction, and the plurality of semiconductor components are arranged on the circuit board in such an arrangement that in terms of a cross-section orthogonal to the flow direction, a ratio of a cross-sectional area of a clearance at a downstream part of the flow of the cooling medium to a cross-sectional area of the tunnel is smaller than a ratio of a cross-sectional area of a clearance at an upstream part of the flow of the cooling medium to the cross-sectional area of the tunnel, the cross-sectional area of the clearance at the upstream part being defined by subtracting from the cross-sectional area of the tunnel a cross-sectional area at the upstream part occupied by the heat sinks that block the flow of the cooling medium, the cross-sectional area of the clearance at the downstream part being defined by subtracting from the cross-sectional area of the tunnel a cross-sectional area at the downstream part occupied by the heat sinks that block the flow of the cooling medium, and wherein a place at which the plurality of the semiconductor components are mounted is divided into at least three regions with respect to a direction of the flow of the cooling medium, space parts (61, 60; 140, 141, 142) are formed between the at least three regions, respectively, and as the space part is located at the more downstream side, the space part becomes wider.