We present the design, fabrication, and characterization of surface micromachined on-chip 3-D air-core arch-shape solenoid microinductors. Combinations of unique surface micromachining fabrication process techniques, such as deformation of polymeric sacrifical molds and conformal electrodeposition of photoresist molds on nonplanar sacrificial polymer mounds, are utilized. An air gap inserted between the inductor's body and the substrate is used to reduce the degradations of high-frequency inductor performances. Fabricated inductors are characterized and modeled at high frequencies from S-parameter measurements. ABCD parameters, derived from measured S parameters, are translated into a simplified physical π model. The resulting 2-, 3-, and 5-turn arch-shape suspended air-core solenoid inductors have inductances between 0.62 to 0.79 nH, peak quality (Q) factors between 15.42 to 17 at peak-Q frequencies between 4.7 to 7.0 GHz, and self-resonant frequencies between 47.6 to 88.6 GHz.