A light sensitive semiconductor package and a fabrication method thereof are provided in which a chip is mounted on a chip carrier and encompassed by a dam, and an infrared filter is attached to the dam to hermetically isolate the chip from the atmosphere. An encapsulant is formed on the chip carrier and surrounds the dam, and a lens is supported by the encapsulant to be positioned above the infrared filter. This allows light to penetrate through the infrared filter and lens to reach the chip. Before forming the encapsulant and mounting the lens, the semi-fabricated package with the chip being hermetically isolated by the infrared filter and dam is subject to a leak test, allowing a semi-fabricated package successfully passing the test to be formed with the encapsulant and lens, so as to reduce fabrication costs and improve yield of fabricated package products.