A semi-block style letter is a less formal version of a block or a full-block letter with the differences being the sender's address, date, reference or attention line and complimentary closing. In addition, the signature lines are located direct center or slightly right of center. The semi-block style is also called modified semi-block because it is a modified version of the block or full block style.
The date is typed on the same line as the reference. Where there are two references, the date is typed on the same line as Our Ref., aligned with the sender's address. Open punctuation.