An experimental study of the dc breakdown voltage for planar MEMS interdigitated aluminum electrodes with gaps ranging from 10 to 500 micron is presented. Unlike most research on the breakdown in MEMS electrodes that was performed at atmospheric pressure, this work focuses on the effect of gas pressure and gas type on breakdown voltage, because this is central for chip-scale plasma generation and for reliable operation in aerospace applications. The breakdown voltage is measured in helium, argon, and nitrogen atmospheres for pressures between 10^2 to 8.10^4 Pa (1 to 800 mbar). For higher values of the pressure P, or of the gap d (i.e., for high values of the Paschen reduced variable P_red=P·d), classical Paschen scaling is observed. For lower values of P_red, however, significant deviations are seen: the Vbd versus. Pd curve shows an extended flat region rather than a narrow dip. These differences cannot be attributed to field emission, but are due to the many length scales effectively present in a planar geometry (on-chip and even off-chip) that leads to the superposition of several Paschen curves. Guidelines are formulated for low-pressure operation of MEMS to avoid or encourage breakdown.