Grain morphology, crystal structure and transistor characteristics of pentacene films have been studied using molecular beam deposition under various conditions: growth temperature ranging from - 5 to 80 degreesC and growth rate from 0.15 to 2 nm/min. Grain morphologies observed with atomic force microscopy are categorized into five groups, which are summarized in a phase diagram. Above the growth temperature of 40 degreesC, many 'recessed regions' which extend independently of molecular steps are observed on the film surfaces. Carrier mobilities of the films estimated from transistor measurements are distributed from 1 x 10(-5) to 0.20 cm(2)/Vs. A comparative study between the structural and electrical results indicates that the mobility does not explicitly depend either on grain size or on specific grain morphology. Lamellar grains associated with flat-lying molecules among differently oriented grains, gaps between grains and the recessed regions are considered to restrict the overall carrier mobility. (C) 2004 Elsevier B.V. All rights reserved.