We measured the lattice and subband electronic temperatures of terahertz quantum cascade devices based on the optical phonon-scattering assisted active region scheme. While the electronic temperature of the injector state (j=4) significantly increases by △T=Te 4 -TL ∼40 K, in analogy with the reported values in resonant phonon scheme (△T ∼70-110 K), both the laser levels (j=2,3) remain much colder with respect to the latter (by a factor of 3-5) and share the same electronic temperature of the ground level (j=1). The electronic population ratio n2/n1 shows that the optical phonon scattering efficiently depopulates the lower laser level (j=2) up to an electronic temperature Te ∼180 K. © 2013 Optical Society of America. ; peer reviewed: yes ; system details: This record was machine loaded using metadata from Scopus ; NRC Pub: yes