a source region;

a drain region;

a semiconductor channel provided between the source region and the drain region and having a thin-line portion of a width W and a length L, the width W and the length L satisfying W≤(π/10(μm²))/L;

a tunnel insulation film provided on the semiconductor channel; and

a conductive fine particle group containing a plurality of conductive fine particles provided on the tunnel insulation film with a surface density not less than 2.5×10¹¹ cm⁻², the conductive fine particles being charge and discharge by electrons tunneling through the tunnel insulation film, the conductive fine particle group being formed over the semiconductor channel; and

a gate region provided over the conductive fine particle group,

wherein the following inequalities are satisfied:

LWD_dot≧[R_Tunnel/R_Tunnel(Tox=0.8 nm)]^{0.3 nm/T}×exp[0.3 nm×(0.8 nm/T)×(4π(2m×3.1 eV)^1/2/h)],

(q/4π∈T)≧26 mV,

[D_dot×d^4/3/(W×L^1/2)]×[R_Tunnel/R_Tunnel(Tox=0.8 nm)]^−2/3≧8000×2^1/2(μm^−13/6)

where D_dot represents the surface density of the conductive fine particles, d an average diameter of the conductive fine particles, T a thickness of the tunnel insulation film, R_tunnel a tunnel resistance of the tunnel insulation film per unit area, R_tunnel (Tox=0.8 nm) a tunnel resistance, per unit area, of a tunnel oxide film with a thickness of 0.8 nm, h Plank's constant, q elemental charge, m an effective mass of a tunnel via the tunnel insulation film, and ∈ a dielectric constant of the tunnel insulation film.