according to wikipidia:
Before the adoption of the present script, Hebrew was written by the ancient Israelites using the paleo-Hebrew alphabet. During the 3rd century BC, Jews began to use a stylized form of the Aramaic alphabet,[1] The present “square script” Hebrew alphabet is a stylized version of the Aramaic alphabet which was adopted from that used by the Persian Empire.The Aramaic alphabet is historically significant, since virtually all modern Middle Eastern writing After the fall of the Persian Empire, Jews used both scripts before settling on the Aramaic form. For a limited time thereafter, the use of the paleo-Hebrew script among Jews was retained only to write the Tetragrammaton, but soon that custom was also abandoned.