Provided are a thermal base generator which is capable of performing cyclization of a. thermosetting resin at a low temperature and with which a thermosetting resin composition having excellent stability can be prepared, a thermosetting resin composition, a cured film, a cured film manufacturing method, and a semiconductor device.The thermal base generator includes at least one selected from an acidic compound which generates a base in a case of being heated to 40° C. or higher, and an ammonium salt containing an anion having a pKa1 of 0 to 4 and an ammonium cation. The acidic compound is preferably an ammonium salt and/or a compound represented by the following General Formula (1), in which A1 represents a p-valent organic group, R1 represents a monovalent organic group, L1 represents an (m+1)-valent organic group, m represents an integer of 1 or more, and p represents an integer of 1 or more.