Poly(dimethylsiloxane) (PDMS) is the most widely used stamp material in soft lithography. Usually, it is thermally vulcanized and can't satisfy all the demands of the resolution, purity and solvent compatibility. In this work, high energy gamma rays are used to crosslink the PDMS base to fabricate stamps designed for soft lithography without the use of a catalyst. PDMS stamps fabricated in this way have several advantages including high resolution, purity and solvent resistance. The PDMS stamp crosslinked at an absorbed dose of 800 kGy has a roughness of 0.18 nm in blank area and can replicate features with the height of 1.1 nm. The amount of uncrosslinked molecules in the bulk of the stamp is only half of that of the 'standard' stamp (made by Sylgard™ 184 at the base/cure agent ratio of 10). Furthermore, the shear elastic modulus of stamps made by radiation induced crosslinking increases with the absorbed dose in the range of 400 kGy to 800 kGy and is higher than that of 'standard' stamps. By measuring the glass transition temperature and calculating molecular weights between crosslinkers, we conclude that the enhancement of stamps' quality can be ascribed to the increase of crosslinking density under gamma ray irradiation.