This paper, for the first time, presents a lateral tunneling transistor based on a two-dimensional boron nitride (BN) and hexagonal boron-carbon-nitrogen (hBCN) heterostructure. The device operation is analyzed based on a nonequilibrium Greens Function (NEGF) method and an atomistic tight-binding (TB) model. The TB hopping parameters are achieved by fitting the bandstructure to density functional theory (DFT) results. This model has been used to calculate the electrical characteristics of the device, such as I ON /I OFF ratio, subthreshold swing, and intrinsic gate-delay time. The results indicate a switching ratio of over eight orders of magnitude, much higher than the previous two-dimensional lateral or vertical tunneling transistor. Also, the device exhibits a low subthreshold swing of 42.17 mV/decade. The results show that the BN and BC 2 N conduction band edge (CBE) and valence band edge (VBE) play important roles in the electrical behavior of the device.