Graphene has a monolayer crystal structure formed with C-atoms and has been used as a base layer of HETs (hot electron transistors). Graphene HETs have exhibited the operation at THz frequencies and higher current on/off ratio than that of Graphene FETs. In this article, we report on the preliminary results of current characteristics from the HETs which are fabricated utilizing highly doped Si collector, graphene base, and 5 nm thin Al2O3 tunnel layers between the base and Ti emitter. We have observed E-B forward currents are inherited to tunneling through Al2O3 layers, but have not noticed the Schottky barrier blocking effect on B-C forward current at the base/collector interface. At the common-emitter configuration, under a constant VBE between,0~1.2V, Ic has increased linearly with VCE forVCE＜VCE indicating the saturation region. As the VCE increases further, a plateau of Ic vs. VCE has appeared slightly at VCE-VBE, denoting forward-active region. With further increase of, has kept increasing probably due to tunneling through thin Schottky barrier between B/C. Thus the current on/off ration has exhibited to be 50. To improve hot electron effects, we propose the usage of low doped Si substrate, insertion of barrier layer between B/C, or substrates with low electron affinity.