Why are semi-synthetic penicillins more widely used instead of the natural penicillin g?

The several kinds of penicillin synthesized by various species of the mold Penicillium may be divided into two classes: the naturally occurring penicillins (those formed during the process of mold fermentation) and the semisynthetic penicillins (those in which the structure of a chemical substance-6-aminopenicillanic acid-found in all penicillins is altered in various ways). Because it is possible to change the characteristics of the antibiotic, different types of penicillin are produced for different therapeutic purposes.