The material processing by DUV laser region has been required for wide band gap material and precise hole and groove in DUV region. It is still very hard to get high power solid-state lasers in this spectral region especially below 300 nm. The rare-gas halide excimer lasers are only the solution, and now the time has come to examine the new applications of material processing with DUV excimer lasers. We have developed several types of DUV excimer lasers. One of them is a high power 248 nm excimer laser with free spectrum operation. The 248 nm excimer laser can be applied to the process of organic materials for semiconductor packages. We are developing the processing of organic materials by 248 nm excimer laser. The organic materials are processed directly by the irradiation using the mask by 248 nm excimer laser. In this method, it is possible to process fine patterns and various patterns. We processed using Ajinomoto build-up films (ABF) as organic material. The types of ABF were GX92, GX-T31 and GY50, and their thickness was 10 μm. We confirmed that it is possible to process via of 5 μm or less in build-up film. Furthermore, it was confirmed that the L/S pattern can be processed. We will report the result of processing organic materials with 248 nm excimer laser.