A resonant tunneling diode (RTD) is considered to be a promising millimeter- and submillimeter-wave source. It is currently the fastest solid-state active device, with the highest reported frequency of oscillaaon above 700 GHz, but with a very low output power. Connecting several tunneling diodes (RTD's or tunnel diodes) in series was shown to be a feasible method for increasing the output power of oscillator circuits using these devices. In this paper, design and excitation of oscillators with several tunneling diodes connected in series is studied theoretically and experimentally. The DC instability of the series connection of tunneling diodes and its effects on biasing are explained. Several solutions to the biasing problem are discussed. A simple large signal diode analysis is used to calculate negative differential conductance, output power, high frequency cutoff and other parameters as a function of the oscillation amplitude. Based on the large signal analysis, oscillators with several tunneling diodes in series were designed and tested. The biasing problem was successfully solved using an extemal RF source to trigger the oscillation. RF triggering was demonstrated in proof-of-principle experiments at microwave frequencies, for oscillators with several tunnel diodes connected in series.