Abstract. In this work we report on short wavelength temperature gradient driven modes that are unstable for large values of the Larmor radius parameter. A new instability is found in this region due to the non-Boltzmann plasma density response for modes whose frequency increases with the wave vector slower than a linear function. Instability is investigated with local and non-local differential equation eigen-mode analysis and confirmed with analytical model. Mode extends over to the region of the electron skin-depth and affects the electron energy transport. In toroidal plasma short wavelength modes match to the ubiquitous mode requiring trapped electrons.