We have fabricated new polycrystalline silicon (poly-Si) thin film transistors (TFTs) with a single grain-boundary by a simple excimer laser annealing (ELA) method which employs a selectively floating amorphous silicon (a-Si) active layer and Al patterns. A thermally insulating air-gap between the floating a-Si and substrate successfully induces the lateral grain growth. The proposed poly-Si TFT exhibits high mobility of 331 cm(2)/V s due to the high-quality grains. The other proposed method employs a lateral grain growth phenomenon obtained by excimer laser irradiation on an a-Si layer with pre-patterned aluminum film. The aluminum patterns act as a masking layer of incident laser beam for the selective melting of a-Si layer. The n-channel poly-Si TFT fabricated by the proposed method shows considerably improved I-V characteristics, such as high field effect mobility exceeding 240 cm(2)/V S. (C) 2002 Elsevier Science B.V. All rights reserved.