Recent developments in the fabrication and simulation of prototype silicon-on-insulator (SOI) microdosimeter arrays are presented. A new planar array design has been proposed which has a number of advantages over the previous elongated parallelepiped and cylindrical mesa array designs. This novel planar array design, which incorporates a guard ring, is based upon 2500 planar cylindrically shaped p-i-n detectors and was fabricated via dopant diffusion and ion implantation. The dopant-diffused arrays were successfully fabricated and tested using 2 mum and 10-mum- thick SOI substrates. Technology computer-aided design modeling of the ion-implanted structure is presented which includes the electrostatic potential profile, showing possible avalanche signal multiplication around the n+ core of the microdosimeter. The alpha particle charge transient response was simulated to determine the charge collection in the sensitive region.