A microlens is one of the most important components in optical microsystems. In the last decade, a lot of attempts have been done to fabricate a microlens or microlenses array, however, most of them are relatively complicated in the fabrication process and have difficulties in getting good surface roughness and realizing microlenses array. In this paper, we represent a very simple fabrication technology of the microlens or microlenses array which is based upon a deep X-ray exposure and a thermal treatment of a resist, usually PMMA. The molecular weight and T<SUB>g</SUB> of PMMA is reduced when it is exposed to the deep X-ray. The microlens is produced through the effect of surface tension and reflow by adding a thermal treatment on the irradiated PMMA. A configuration of the microlens is determined by parameters such as absorbed X-ray dose on PMMA, heating temperature, and heating time in the thermal treatment. Diameters of the produced microlens range from 100 micrometers to 1500 micrometers and their changed heights are between 10 micrometers and 20 micrometers .