High power impulse generators, with picosecond pulse duration, are very important for wide band radar application. By constructing a nonlinear transmission line (NLTL) with a novel lateral stacking configuration and barrier stacked heterojunction devices, we report that impulses with up to 35 V pulse amplitude, which is equivalent to 12 W for a 50 SI line, and r:.1 8.5 ps FWHM pulse duration can be achieved. Lateral stacking can double or triple the signal amplitude, depending on the level of lateral stacking introduced. Calculations show that for a NLTL with a final pulse width > 8 ps, we can laterally stack up to a factor of two without introducing significant parasitics. In addition, we can quasi-optically power combine the output of four such lines on a 2 inch wafer, resulting in 48 W total output power. In proof-of-principle experiments, two single lines have been designed and will be fabricated. One is a 40 section tapered coplanar strip line with the first 28 sections employing the lateral stacked structure and bow-tie antennas as input and output. The input is a signal with 18 V amplitude and pulse width between 100 ps to 200 ps, while the predicted output is an impulse with 26 V amplitude 6.76 W) and 8 ps pulse duration. The second line is a 30 section tapered coplanar wave guide, suitable for probing, with input signal of 22 V amplitude and 100 to 200 ps pulse duration and the predicted output signal of 35 V amplitude (e:i 12.3 W) and 20 ps pulse duration.