In the manufacture of thermoelements from n-type Bi2Te2.7Se0.3 crystals usually electroerosion cutting is applied, which leads to formation of disturbed in composition and structure surface layer on the branches. Such disturbed surface layer significantly reduces the thermoelectric figure of merit of the branches [1, 2]. In the present work we investigated the effect of surface treatment of Bi2Te2.7Se0.3 samples on their electrical conductivity, the coefficients of thermoelectric power  and surface conductivity  in the 77 ÷ 300 K temperature range.  Samples of the parallelepiped form with dimensions 12х6х3 mm3 for research were cut using electroerosion cutting from ingots of crystals of the specified materials of cylindrical shape with a diameter of  ~ 14 mm. Measurements of the specified parameters were carried out on samples immediately after cutting of ingots and in the same samples after treatment of their surfaces by mechanical grinding, chemical or electrochemical etching.     The results are shown in the Table. The table shows that at surface treatment the values of s  and 2 are subjected to significant changes.      Table. Variation of the conductivity (/0), coefficient of  thermoelectric power (/0),   parameter (2/020), and surface conductivity  (s/s0 ) of samples Bi2Te2.7Se0.3 at the processing of their surfaces (all values with an index 0 were measured before the surface treatment)   Samples based  on Bi2Te2.7Se0.3   crystals Processing method Т,К /00 2/02 (s/s0) Mechanical polishing 77 1,19 1,06 1,20 0,11 300 1,41 0,93 1,21 0,95 Chemical  etching 77 0,95 1,01 0,99 0,12 300 0,96 1,06 1,08 0,94 Electroсhemical etching 77 1,19 0,99 1,16 0,13 300 1,30 0,95 1,17 1,31   When cutting crystals Bi2Te2.7Se0.3 to samples, on the cut surface disturbed layer of 5-15 microns thick occurs [1]. It was found [3] that disturbed layer consist of mainly of two sublayers with different composition: sublayer formed by melting and partial combustion of the semiconductor material in spark cutting, and hardening the liquid phase, highly contaminated with electrodes products and the dielectric medium. It is shown that the disturbed layer significantly reduces α ₂ σ               of Bi2Te2.7Se0.3 samples. This is due primarily low conductivity surface layer in comparison with the conductivity of the crystal itself. The methods of removing the disturbed layer resulting in increase of α ₂ σ value.