"hu" is pronounced [w] only if a vowel comes next, therefore the "h" is silent and "u" is pronounced [u].
Finally, the semivowels [j] and [w] can be assigned to the phonemes /i/ and /u/, as there are no minimal contrasts in Spanish between the sounds [i] and [j] or between [u] and [w]. Thus the semivowels can be seen as the forms taken by /i/ or /u/ when they occur in a diphthong with another vowel. Each semivowel can occur immediately before or immediately after the vowel with which it forms a diphthong, as is shown in Table 2 below.
Table 2 Distribution of the semivowels [j] and [w]
"hu" is pronounced [w] only if a vowel comes next, therefore the "h" is silent and "u" is pronounced [u].
Table 2 Distribution of the semivowels [j] and [w]
https://www.staff.ncl.ac.uk/i.e.mackenzie/conssemi.htm