  In this article we present a 3-dimensional analogue of a well-known theorem
of E. Bombieri (in 1973) which characterizes the bi-canonical birationality of
surfaces of general type. Let $X$ be a projective minimal 3-fold of general
type with $\mathbb{Q}$-factorial terminal singularities and the geometric genus
$p_g(X)\ge 5$. We show that the 4-canonical map $\phi_4$ is {\it not}
birational onto its image if and only if $X$ is birationally fibred by a family
$\mathscr{C}$ of irreducible curves of geometric genus 2 with $K_X\cdot C_0=1$
where $C_0$ is a general irreducible member in $\mathscr{C}$.
