Code39 standard also specifies a way to print characters outside the native Code 39 character set. It does so by encoding these characters with two native Code 39 characters. Four characters, the percent sign (%), dollar ($), slash (/) and plus sign (+) are used as leading characters.

Since these leading characters are also in the native Code 39 character set, the barcode reader is unable to determine whether a barcode is Code 39 extended or just normal code 39. For example, a barcode reader may read the extended code 39 barcode abc as +A+B+C. Fortunately, most scanners allow you configure if you expect a Code 39 extended symbol (sometimes called Code 39 Full ASCII), or just a normal code 39 symbol.

When you need to encode characters outside the native set, use the table below. For example, the sequence for lower case letter a is +A.

To create barcode string for extended code39, first convert character outside the code39 set to two characters. Add start/stop character at the beginning and the end. Formatting the result with a code39 font will result in an extended code 39 barcode.