A touch sensor device is provided. The touch sensor device includes a substrate having a sensing region and a non-sensing region. There is a plurality of sensor electrodes disposed on the surface of the substrate in the sensing region. At least one of the sensor electrodes has a sidewall with a concave-convex contour. The concave-convex contour includes a first convex portion, a second convex portion, and a concave portion between the first convex portion and the second convex portion. The first convex portion is closer to the surface of the substrate than the second convex portion, and the first convex portion is more outward than the second convex portion. A method for forming the touch sensor device is also provided.