This paper presents a newly developed square law detector array whose NEP is as low as ∼ 1 pW/Hz0.5 for 1.0 THz waves. The detector array using high electron mobility transistor (HEMT) with InGaAs/InAs/InGaAs double hetero-structured channel has been fabricated. The InAs-HEMT was fabricated on a quartz substrate using the layer transfer technology. Also, an array of square law detectors was developed by applying advanced selective etching, atomic layer deposition, and metallization to the transferred hetero-structured layers. The static analysis revealed that the transistor shows electron mobility as high as 3,200 cm2/Vs and low leakage with subthreshold slope as low as ∼ 100 mV/dec. Detection performance was characterized by directly inputting 1.0 THz waves thorough a THz probe to each of the arrayed detectors. It is also demonstrated that the detection characteristics were well described by the analytical formulae derived from the channel-carrier behavior model. The experimental results suggested that the developed detector array is a promising candidate for imaging application.