In this work, the fabrication, the electrical and optical characterization of red organic light emitting transistors using thin film made of alumina grown by atomic layer deposition (ALD) coupled with PMMA (poly(methyl-methacrylate)) as gate dielectric material are reported. Use of ALD-grown Al2O3 is shown to greatly reduce the operation range and the threshold voltage in this class of devices as compared to polymer-based dielectric counterpart, while at the same time comparable optical performances are maintained. Further, reducing the oxide layer thickness demonstrates the possibility of fine tuning the device working conditions, while maintaining optoelectronic performances, robustness and very low leakage current.