In this paper, microstrip stepped-impedance hairpin resonator (SIR) low-pass filter (LPF) and slow-wave band-pass filter (BPF) using dielectric supported air-gapped microstrip line (DAML) of surface micromachining on GaAs substrate are proposed. The DAML structure, which is a new low-loss micromachining transmission line, is useful for the integration of MEMS and/or MMIC components. Design parameters for the proposed SIR low-pass and slow-wave band-pass filters are derived based on stepped-impedance theory. The proposed slow-wave BPF is designed to produce a passband of 10% at the fundamental frequency of 60 GHz. and a new SIR LPF with aperture and IDC (inter-digital capacitor) is designed for 3-dB cutoff frequency of 33 GHz. The measurement results of the BPF filter and LPF filter agree well with simulation results. These filters are useful for many millimeter-wave system applications.