A study on CMOS interconnections lines up to 40GHz is presented. The lines propagation constant γ and impedance characteristic Z0 are obtained from the measured S parameters up to 40 GHz, on test structures with different lengths, with or without metal ground plane. The values of the well-defined transmission line RLGC lumped model elements per unit length for each measured test interconnection lines are obtained. Although, the RLGC elements values are frequency dependent, we show that using constant values in a wideband, from 5 GHz to 40 GHz, the interconnections model is in good agreement with the experimental S parameters, validating the modelling technique. As expected, for shorter lines, one RLGC section is adequate to attain a good agreement with measured values. However, for longer lines, the number of RLGC sections must be increased. For low frequencies the accuracy is better for interconnections lines with metal ground plane. However, for high frequencies (f > 15 GHz) the accuracy is good for both type of interconnection lines.