Electrical sampling with a temporal resolution of less than 500 fs has been achieved using coplanar transmission lines on electro‐optic substrates. The improved performance over the previously demonstrated balanced stripline is due to the reduced dimensions, i.e., distance between the electrodes and width of the electrodes, achievable with photolithographic technique. By further reducing the line dimensions to 10–20‐&mgr;m range, this technique makes the temporal resolution of electrical waveforms in the range of 100 fs possible.