This paper introduces a new method to calculate the spatial variation of the Standard Effective Temperature (SET) in a three-dimensional idealized urban area. The SET is a thermal comfort index that describes human sensation in the urban environment. It derives the SET by modeling the mean radiant temperature, urban area visibility, building shade area and two-nodes SET model. The major novelty of this paper is a matrix-based model for the SET. Spatial SET prediction is evaluated at the pedestrian level (1.5 m from the ground) in an idealized urban area in a clear summer day of San Diego, California. CFD simulations of flow field coupled with heat transfer used for obtaining urban surface temperature, wind velocity and air pressure. This study reveals that SET has a high variability in the horizontal directions within a small urban area. This method is still under development