We have previously derived the relationship between electron mobility and current density J = J e + J h = ( e n μ μ e + e p μ μ h ) E Now Ohm's law can be written in the form J = σ σ E where σ σ is defined as the conductivity. Therefore we can write down: σ σ = e n μ μ e + e p μ μ h which can be factorised to σ σ = e ( n μ μ e + p μ μ h )