Well-characterized test conditions are essential for validating the engineering design of an adaptive optical system. A technique for fabricating high-resolution, well- characterized pseudo-random phase plates that addresses this need is described. Among other uses, these phase plates can be used to test adaptive optics systems under controlled conditions. Machining a surface whose relief height is proportional to the desired phase forms a pixellated phase plate. Using Lexitek's Near-Index-MatchTM approach, a sandwich of two materials is formed that produces the desired phase. Phase plates with 20 micron pixels have been fabricated using a 4096 X 4096 pixel grid. Results are presented.