A two step process has been developed for the fabrication of diffraction limited concave microlens arrays. The process is based on the photoresist filling of melted holes obtained by a preliminary photolithography step. The quality of these microlenses has been tested in a Mach- Zehnder interferometer. The method allows the fabrication of concave microlens arrays with diffraction limited optical performance. Concave microlenses with diameters ranging between 30 μm to 230 μm and numerical apertures up to 0.25 have been demonstrated. As an example, we present the realization of diffusers obtained with random sizes and locations of concave shapes. © 2008 Optical Society of America OCIS codes: (130.0130) Integrated optics, (220.0220) Optical design and fabrication.