  Stripe phases, in which the rotational symmetry of charge density is
spontaneously broken, occur in many strongly correlated systems with competing
interactions. One representative example is the copper-oxide superconductors,
where stripe order is thought to be relevant to the mechanism of
high-temperature superconductivity. Identifying and studying the stripe phases
in conventional strongly correlated systems are, however, challenging due to
the complexity and limited tunability of these materials. Here we uncover
stripe phases in WSe2/WS2 moir\'e superlattices with continuously gate-tunable
charge densities by combining optical anisotropy and electronic compressibility
measurements. We find strong electronic anisotropy over a large doping range
peaked at 1/2 filling of the moir\'e superlattice. The 1/2-state is
incompressible and assigned to a (insulating) stripe crystal phase. It can be
continuously melted by thermal fluctuations around 35 K. The domain
configuration revealed by wide-field imaging shows a preferential alignment
along the high-symmetry axes of the moir\'e superlattice. Away from 1/2
filling, we observe additional stripe crystals at commensurate filling 1/4, 2/5
and 3/5. The anisotropy also extends into the compressible regime of the system
at incommensurate fillings, indicating the presence of electronic liquid
crystal states. The observed filling-dependent stripe phases agree with the
theoretical phase diagram of the extended Hubbard model on a triangular lattice
in the flat band limit. Our results demonstrate that two-dimensional
semiconductor moir\'e superlattices are a highly tunable platform to study the
stripe phases and their interplay with other symmetry breaking ground states.
