- Crystalline structure, recombination activity, and electron transport properties have been investigated in boron-doped, thin-walled crystals of silicon obtained from hexagons grown by the EFG process (a modification of Stepanov's method). All grain boundaries (GBs) can be divided into special (Σ3, Σ9), near coincidence, highly deviated (Σ3, Σ9, Σ13), and general (i.e., non-special) GBs. Special GBs are electrically inactive to both minority and majority carriers. Near coincidence GBs are active to minority but inactive to majority carriers. General and highly deviated GBs are very active to both minority and majority carriers. The observed classification of GB activity is explained on the basis of a phenomenological model.