# What is the limiting value of band gap that makes a material semiconductor?

What is the limiting value of band gap (in eV) that makes a material semiconductor? Or what is the value of band gap that separates insulator and semiconductor?

• There is no commonly accepted definition. If you can make a standard semiconducting device in the material, it is a semiconductor. – Jon Custer Dec 10 '15 at 13:35

The transition of electron from the valence band to the conduction band is a probabilistic event. Electrons get this excess energy equivalent to the band gap ($\Delta E$) from the thermal energy (kT, where k is the Boltzmann constant and T, temperature in Kelvin). Hence, the probability of such an event will be proportional to $e^{-\Delta E/kT}$.
Answering your question, although there is no standard defined value of band gap, you can see since it's an exponentially falling smooth curve that one can define a cutoff $\Delta E$, saying that for band gap > $\Delta E$ there are practically no electrons transiting to the conduction band, qualifying the material as an insulator (i.e., exhibiting insulator-like properties).