Wiring substrate and semiconductor device

A wiring substrate comprising:

• a first wiring layer;
• a first insulation layer that is formed from an insulative resin and covers the first wiring layer;
• a second wiring layer located on an upper surface of the first insulation layer;
• a second insulation layer that is formed from an insulative resin and covers the first insulation layer and the second wiring layer;
• and
• a via wiring layer that extends through the first insulation layer and connects the first wiring layer to the second wiring layer, wherein the via wiring layer includes an upper end surface that is connected to the second wiring layer and flush with the upper surface of the first insulation layer, wherein
• the second wiring layer has a higher wiring density than the first wiring layer,
• the first insulation layer includes
• a first resin layer that contains a filler, and
• a second resin layer that is located on an upper surface of the first resin layer and has a lower filler content rate than the first resin layer,
• an upper surface of the second resin layer is the upper surface of the first insulation layer, and
• the upper surface of the first resin layer is a curved surface that is upwardly curved toward the upper end surface of the via wiring layer.