Streaming plasma instability at near ballistic electron motion in InN n(+)n(-)nn(+) structures is theoretically investigated. At low lattice temperatures (T < 140 K), when dominating scattering mechanism in InN is the opticall phonon emission the electron transport through the structure, of certain geometry can be essentially nonstationary in some bias range. By Monte Carlo particle technique the steady state transport and microwave power generation in InN n(+)n(-)nn(+) structures connected with external parallel resonant circuit, are simulated. It is demonstrated that over hundred microwave of the microwave power can be delivered by the structure in 1.1 similar to 1.2 THz frequency range at liquid nitrogen temperature.