The point (0, 3) in rectangular coordinates is converted to polar coordinates as follows:
1. **Calculate the radius \( r \):**
\[
r = \sqrt{x^2 + y^2} = \sqrt{0^2 + 3^2} = \sqrt{9} = 3
\]
2. **Determine the angle \( \theta \):**
- Since \( x = 0 \), the point lies on the positive \( y \)-axis.
- The angle \( \theta \) for points on the positive \( y \)-axis is \( \frac{\pi}{2} \) radians (90°).
**Final Answer:**
\[
\boxed{(3, \frac{\pi}{2})}
\]