We present details on the high-frequency behavior of a downscaled 2 mum wide microstrip line, fabricated with both signal and ground conductors on top of the substrate. A significantly reduced geometric dispersion for electric pulses with a bandwidth of several hundred gigahertz is found in time-resolved electrooptic sampling measurements. Additionally, the strong confinement of the electric field within these surface-mounted microstrip lines promises low substrate losses, even on doped substrates, and reduced crosstalk.