Abstract Utilization of the zero space microlens technology can significantly improve the image quality of CMOS sensors. In this study, we present systematical data of design, simulation, characterization and silicon level testing during the initial stage of development of the zero space microlens based CMOS imaging technology. The optimal structure of zero space microlens was obtained based on the simulation results. Sample CMOS image sensors with a 2.8 μm pitch zero space microlens above each pixel have been successfully fabricated based on 0.18 μm CMOS technology. Using AFM (atomic force microscopy) and sensor test platform, the structural and optical properties of both space microlens and zero space microlens have been characterized, and their performances have been evaluated respectively. Both AFM results and silicon tests have demonstrated that the 2.8 μm pitch zero space microlens can remarkably improve the pixel sensitivity and pixel array non-uniformity, and reduce the optical crosstalk. Compared to the space 2.8 μm square microlens, the zero space microlens shows 78.83% (68.42% and 75.93%) enhancement of photosensitivity and increment of pixel non-uniformity up to 20% (45.6% and 30.77%) for R (G and B), and reduction of the optical crosstalk up to 44.49%, under 45 lux light and 30 ms exposure time. In addition, the zero space microlens has also shown a great potential in further reducing pixel size down to less than 2.8 μm and meanwhile improving imaging performance of CMOS image sensors.