A trimming process by a laser beam is disclosed. The trimming process comprises two steps. In a first step, a laser shield layer is formed over an untrimmed region of a trimmed material adjacent to a trimmed region. The laser shield layer has a higher heat conductivity than the trimmed material and a large reflectivity for laser beam. In a second step, the trimmed material is cut off. To cut off, a laser beam is applied onto the upper surface of the trimmed region of the trimmed material to vaporize the trimmed material in the trimmed region.