metal chalcogenide (Ag

Pb

Bi)(S

Se

Te) with an NaCl-type structure was designed by multi-site-type high-entropy alloying (MST-HEA)

and the thermoelectric properties were investigated. In this material

both cation and anion sites were alloyed and thus its total entropy of mixing Δ

S

mix

(total) achieved 2.00

R

(

R

: gas constant). It was found that present sample is an n-type semiconductor with ultra-low lattice thermal conductivity (

κ

L

) of 0.62 Wm

−1

K

−1

at room temperature and 0.46 Wm

−1

K

−1

at

T

 = 723 K. Very low

κ

L

and good power factor resulted in figure of merit of 0.54 at

T

 = 723 K.