A semiconductor device includes a bottom electrode, a top electrode, a sidewall spacer, and a data storage element. The sidewall spacer is disposed aside the top electrode. The data storage element is located between the bottom electrode and the top electrode, and includes a ferroelectric material. The data storage element has a peripheral region which is disposed beneath the sidewall spacer and which has at least 60% of ferroelectric phase. A method for manufacturing the semiconductor device and a method for transforming a non-ferroelectric phase of a ferroelectric material to a ferroelectric phase are also disclosed.