Friction loss and heat transfer enhancement measurements were obtained for double-sided, partial height, strip fin arrays within a high aspect ratio (AR = 8), rectangular channel. Fins were arranged in a staggered array configuration with channel height to fin thickness ratio H/W = 9.6, spanwise spacing distance to fin thickness ratio S/W = 8.0, and streamwise spacing distance to fin length ratio X/L = 1.0. Shortened strip fins of equal length are positioned directly opposite of each other on the upper and lower channel surfaces with three gap size to channel height ratios considered G/H = 0.2, 0.3, and 0.4. The thermal performance of each fin configuration is determined from the measured pressure drop across the array and regionally averaged heat transfer coefficients at flow Reynolds numbers ranging from Re = 20,000–80,000. The partial height strip fin results are compared to baseline cases of strip fins spanning the full height of the channel and the smooth channel without roughness elements. Linear correlations of friction loss and power correlations of the heat transfer enhancement and thermal performance are provided as functions of flow Reynolds numbers for all cases. Strip fins spanning the full height of the channel provide the greatest heat transfer enhancement of all cases but introducing a gap size can significantly reduce friction losses. Full height strip fins provide the greatest thermal performance for Reynolds numbers ranging from Re = 20,000–30,000, and partial height strip fins with the gap size of G/H = 0.3 provide the greatest thermal performance for flow Reynolds numbers ranging from Re = 40,000–80,000.