Pulsed-mode high-power generation in silicon double drift region (DDR) IMPATT devices is briefly reviewed, and current work is presented on the structural parameter dependence of pulsed silicon IMPATTs designed for operation around 94 GHz at a current density of 100 kA cm-2. Computer studies are presented on three DDR structures: (i) flat, (ii) SLHL, i.e. low-high-low structure with single bump on either side of the p-n junction, and (iii) DLHL, i.e. low-high-low structure with double bumps on either side of the p-n junction. The results indicate that the DLHL structures exhibit much higher negative conductance than the other structures. It is seen that the magnitude of the peak negative conductance of the DLHL DDR IMPATT devices decreases appreciably if low-high-low bumps are changed from rectangular to trapezoidal shape. It is also found that the heights of the second bumps produce little variation in the negative conductance of the DLHL device, although the second bumps play a vital role in containing the space-charge effect at high current densities. The heights of the first bumps close to the metallurgical junction, however, produce appreciable changes in the small-signal behaviour of the DLHL diodes. Further, it has been found that the width of the active region, if increased gradually, makes the DLHL diode a narrow band device operating near the avalanche resonance frequency. The effect of variation of bump width and bump location (from the optimized structure) on the high-frequency properties of the device has also been studied and the results are presented in the paper.